Liver function tests
A plasma bilirubin concentration above 300 pmol/l (18 mg/dl) always indicates severe disease ( O'GLadY.etaL 1989). Lower levels do not necessarily preclude the diagnosis or indicate a good prognosis with acetaminophen (paracetamol) poisoning or other situations where the onset of liver failure is rapid. Plasma aminotransferase concentrations (alanine aminotransferase and aspartate aminotransferase) may be grossly elevated (up to 10 000 IU/l). However, increases are time dependent, and relatively normal plasma concentrations of these enzymes may be found if massive hepatic necrosis has occurred before presentation. Non-specific and minor elevations may occur in plasma alkaline phosphatase and g-glutamyl transferase concentrations.
Hypoglycemia is a common but not universal manifestation of ALF. It is important because it is treatable with intravenous glucose. Signs of hypoglycemia may be masked by encephalopathy.
The international normalized ratio (INR) for prothrombin, previously the prothrombin time (PT), is always prolonged. It can be used as an index of disease severity (T.a.b.le.3) provided that fresh frozen plasma has not been given. Levels of all coagulation factors, except factor VIII, are reduced. Low-grade disseminated intravascular coagulation occurs in most patients, probably because of low levels of antithrombin III and protein C. Thrombocytopenia is common.
Table 3 Criteria to identify patients with ALF who are unlikely to survive without liver transplantation
Plasma albumin and globulin concentrations may be normal on presentation. Plasma concentrations of proteins with a shorter half-life synthesized by the liver (e.g.
prealbumin) are decreased. Other laboratory tests
Many other laboratory tests are abnormal in ALF and, although not necessarily diagnostic, may guide management. Common abnormalities include respiratory alkalosis, metabolic alkalosis or acidosis, hypokalemia, hypomagnesemia, hyper- or hyponatremia, and renal failure.
Specific tests to determine the cause of acute liver failure
These are discussed below and summarized in TabJeJ...
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